PLATE 20 



Figs. Smeathenella hamagensis Bancroft 



1, 5. — Dorsal internal mold, and a replica of it which shows 



brachiophores cemented to valve to produce thornlike 

 structures. Cf. fig. 19, Heterorthis clytie. 



2, 4. — Internal mold of crushed ventral valve, and a replica 



taken from it, to show short dental plates. 

 3_ — Replica taken from dorsal exterior mold, showing 



fascicosteUate surface. 

 Ordovician (basal Harnagian), Smeathen Wood, 

 Horderley, E. Shropshire, England. Cat. Nos. 

 S2119, S2120. xl. 



Muscle 



Harknessella vespertilio (Sowerby) 

 6^ 10. — ^Ventral internal mold (10), and replica. 



area lobate. 

 7,9. — Dorsal interna! mold (9), and replica. This wax 

 impression shows clearly the nature of the brachio- 

 phores, although the lobate character of the cardinal 

 process is not altogether clear because of the imper- 

 fection of the impression. The cementing of the 

 brachiophores to the valve is clear, however. Cf. 

 fig. 19. 

 Ordovician (basal Caradocian, Heterorthis fatera 

 grits), Coston District, E. Shropshire, England. 

 Cat. Nos. S2122 (figs. 6, 10) and S 2123. x 1. 



Harknessella sp. 



8. — Dorsal internal mold. 



Ordovician (basal Caradocian, Harknessella subquad- 

 rata zone), BuUhill, Cressage District, E. Shrop- 

 shire, England. Cat. No. S 2124. x 1. 



11, 

 13, 



Reuschella bilobata (Sowerby) 

 14. — ^Ventral internal mold (14) and wax impression 

 taken therefrom, showing character of muscle field. ^ 

 15. — Dorsal internal mold, and replica. Cardinalia 

 close to those of Harknessella. 

 Ordovician (Acton Scott beds). Castle Hill, E. 

 Shropshire, England. Cat. Nos. S2125 (figs. 13, 

 15) and S2126. x 1. 



Reuschella cf. R. bilobata (Sowerby) 



12. — Dorsal exterior, showing coarse costells. 



Ordovician (Caradocian), Cardington, Salop, Eng- 

 land. Cat. No. S 1065. x 1. 



Heterorthis clytie (Hall) 



16, 17. — ^Ventral and dorsal views of exterior. 



Ordovician (Trenton), Bourbon Co., Ky. Cat. No. 

 S1068. X 1.5. 



Figs. Heterorthis clytie (Hall) — Coni. 



18. — Dorsal interior, showing cardinalia. x 1.5. 



19. — Posterior view of specimen in fig. 20, showing small, 

 convex chilidium covering carinate median lobe of 

 cardinal process, x 2. 



20. — Dorsal interior, showing cardinalia, small adductor 

 field, and pallial marks; also cementation of brachio- 

 phores to valve. In Heterorthis and its allies this 

 cementation takes place along the dorsal surface of the 

 brachiophores, but in Dalmanella, Levenea, etc., it is 

 along their flat, inner face. Shown also in this figure 

 is the submarginal elevation in the dorsal valve, and 

 the corresponding depression in the ventral valve 

 can be seen in fig. 21. x 1.5. 



2 1 . — Ventral interior, showing semiflabeUate pattern formed 

 by combined diductor and adjustor scars, x 1.5. 

 Ordovician (Hermitage), Frankfort, Ky. Cat. Nos. 

 S 1067 (figs. 19-21) and S 1074. 



Heterorthis cf. H. altemata (Sowerby) 

 25. — Ventral internal mold, showing elongate diductor and 

 adjustor muscles. 

 Ordovician (Caradocian), W. Corwan, England. 

 Cat. No. S 1073. x 1.5. 



Rhipidomella sp. 



22. — Dorsal interior turned slightly to the side showing 

 cardinalia. Right brachiophore shows an elongate 

 blade-like process extending from a median swelling. 

 Such a process is missing in fig. 23. 

 Locality unknown. Cat. No. S 1220. x 3. 



Rhipidomella vanuxemi (Hall) 

 23. — Dorsal interior, showing swollen cardinal process and 



adductor field. 

 27. — Ventral interior, showing postero-median position of 

 adductor field, and large, semiflabeUate diductor-ad- 

 justor area. 

 Devonian (Hamilton), Canandaigua, N. Y. Cat. 

 No. S 1286. X 1.5. 



Rhipidomella musculosa (Hall) 



24. — Ventral interior, showing unusually expansive devel- 

 opment of diductor-adjustor fields. 

 Devonian (Oriskany), Cumberland, Md. Cat. No. 

 S1193. xl. 



Rhipidomella penelope (Hall) 



26. — Ventral interior of an old shell, showing puckered 

 margins of muscle field and swollen, irregular inner 

 surface. 



Devonian (Hamilton), Canandaigua Lake, N. Y. 



Cat. No. SI 229. x 1. 



234 



